There is little experimental information available on the mechanisms controlling the integration of the constellation of cardiovascular responses produced by average environmental stimulation. Although it is likely that cardiovascular adjustment occur in order to accomodate metabolic demands, the processes involved in the marked cardiovascular changes accompanying emotional states (e.g., anger, rage, fear) need to be elucidated. The present research plan proposes to study the neural control of cardiovascular responses in the rat exposed to a noxious exogenous stimulus complex. An evoked defense response will be produced by presenting an aversive stimulus complex consisting of tone/light and foot shock. The use of pulsed Doppler flow probe technology in the freely moving, awake rat will permit the quantification of hemodynamic changes on a second by second basis in a conrolled behavioral test situation. Using neurobiological and pharmacological methods the afferent, efferent and central mediating neural and humoral components of the response will be characterized. Also cardiovascular responsivity of the stimulus complex will be studied in conjunction with hypertensivogenic manipulations. The results of these experiments will provide fundamental new information on (1) the cardiovasculary dynamics accompanying aversivew stimuli, (2) the mechanisms (humoral and/or neural) mediating cardiovascular adjustments to such stimuli, (3) the role of the central nervous system in the coupling and modulation of somatic and autonomic responses and, (4) the role of the defense reaction in the pathogenesis of hypertension.